This invention relates to a single-stage, sorption-type cryopump (hereafter cryosorption pump) for a pressure range of between 1,000 millibar and 10.sup.-7 millibar and includes a refrigerator connected in a heat transmitting manner with metallic wall surfaces. Further, at the wall surfaces a sorption material is disposed whose temperature--which, during a predetermined desorption period raises approximately to room temperature--is set by means of the refrigerator to approximately 60 K. during the sorption period.
The known cryopumps include metallic wall surfaces which are arranged in a pump vessel and which are cooled by a refrigerator coupled to the pump vessel, for example, in two stages, first to approximately 70 K. and then to 20 K. so that on the wall surfaces the gases and vapors condense and form a solid deposit as described, for example, on page 2993, Volume 10 of the work entitled Lexikon Technik und exakte Naturwissenschaften (Encyclopaedia of Engineering and Exact Natural Sciences), published by Fischer Taschenbuch Verlag, 1972. The known cryopump, however, requires a pre-vacuum of approximately 10.sup.-3 millibar because a cooling at atmospheric pressure would lead to an excessively thick condensate layer which, in turn, would adversely affect the operation of the pump at low pressures. The auxiliary pump which generates the pre-vacuum is an electromechanical pump which necessarily contaminates the vacuum with oil.
In certain applications, it is required to maintain the vacuum rigorously free from oil particles. Thus, in the manufacture of electronic structures in high vacuum, because of the microscopically thin layers which have to be built, the appearance of hydrocarbon molecules causes an approximately 70% waste which significantly increases the manufacturing expenses. Also, similar requirements for an oil-free vacuum apply in the field of fusion technology.
There are known sorption pumps in which gases are absorbed by a sorption material, such as activated carbon. The sorption material is, however, after a predetermined period, saturated with the absorbed gas and consequently the pumping operation has to be suspended in order to regenerate the sorption material. As a result, a high vacuum can be maintained for a longer period only with significant expense, if at all.
As discussed, for example, in the periodical Chemie Ingenieur Technik (Chemical Engineering), Volume 40, 1968, Issue 5, pages 207-213 (published by Verlag Chemie GmbH, Weinheim, Federal Republic of Germany), it is known to combine a cryopump and a sorption pump to form a "cryosorption pump" and to fixedly connect metallic wall surfaces with a molecular sieve. Such an arrangement, however, has the disadvantages of a sorption pump so that the set high vacuum cannnot be maintained during the periods of regenerating the molecular sieve.